Bear in mind that the src and dest fields in the externally-supplied APRS packet (not just a text message) are the values to be placed in the AX.25 sender and destination address fields in the AX.25 packet. This is _not_ the format for command-mode TNC-2 or for APRS-IS packet transmission and reception. If you choose not to specify these, the callsign-SSID of your transmitting port will be the sender (possibly different if you have multiple radio ports for a cross-band digipeater), and whatever tocall you have selected for YAAC (defaulting to APJYC1) will be the AX.25 destination. Note that externally-supplied packets will get the default digipeat path defined by your YAAC configuration (defaulting to WIDE1-1,WIDE2-1); you cannot control this from the external application, but can configure it inside YAAC. Also, after the colon terminating the destination field, the remaining text has to be a valid APRS packet as described in the APRS 1.0.1 Protocol Specification document (such as starting with ! for a position report, or : [again] to indicate a text message with an addressee). So if you are trying to send an APRS text message and you don't have two colons in a row, and then another colon after the addressee callsign, it won't work.
I presume you're using the "src>dst:text" format because you want a different callsign in the sender field than your station callsign. If your regular station callsign and tocall are acceptable, you can use just the format of a plain-text APRS packet without the "src>dst:" prefix. Unless you're acting as a proxy for another station, "src>dst:" probably shouldn't be used, but I assume you need to do that so that SMS messages can come back to the designated DMT station.
Hope this helps.
Andrew, KA2DDO
author of YAAC
